Multi-antenna transmission technology, which is also referred to as Multi-Input Multi-Output (MIMO) technology, can apply MIMO technology that uses multiple transmit antennas and multiple receive antennas to improve data transmission and reception efficiencies. MIMO technology may include spatial multiplexing, transmit diversity, and beamforming. A MIMO channel matrix which is defined according to the number of receive antennas and the number of transmit antennas may be decomposed into a number of independent channels, each of which is referred to as a layer or stream. The number of layers or streams or the spatial multiplexing rate is referred to as a rank.
While the conventional 3GPP LTE system (for example, 3GPP LTE release 8 or 9) supports uplink transmission through a single antenna, a 3GPP LTE-A system (for example, 3GPP LTE release 10), which is an evolution of the 3GPP LTE standard, is under discussion to support uplink transmission through up to 4 transmit antennas.
On the other hand, to efficiently perform downlink multi-antenna transmission, a feedback to a downlink channel may be transmitted from a receiving end (for example, a user equipment) to a transmitting end (for example, a base station). Such feedback information may include a rank indicator (RI) and channel quality information (CQI) of a downlink channel. A Hybrid Automatic Repeat reQuest (HARQ)-Acknowledgement/Negative Acknowledgement (ACK/NACK) which indicates whether or not decoding of downlink data is successful may also be transmitted from the downlink receiving end to the downlink transmitting end. Information such as RI, CQI, and HARQ ACK/NACK information may be collectively referred to as uplink control information (UCI).
UCI may be transmitted through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH). When UCI is transmitted through a PUSCH, the UCI and uplink data may be multiplexed and transmitted.